Selective circuits



C urrenf H. W. 'NiCHOLS SELECTIVE \CIRCUITS Oct. 27,1925- Filed Oct. 29. 1921 Z My Freyuency reamed a. 27, 1925.

UNITED STATES,

R-AATENT orrlce.

' I HAROLD WILLIAM NICHOLS, 0F MAJPLEWO'O D, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INQORPOB ATED, OE NEWJORK, N. Y., A CORPORATION OF NEW YORK.

snnnorrvn omcui'rs.

Application filed October 29, 1821. Serial No. 511,475.

To all who m it 'may concern."

Be it known that I, HAROLD ILLIAar NICHOLS, a citizen ,of the United States,re-

siding at Maplewood, in the county of Es- -'5 sex, State of New Jersey, have invented certain new and useful Improvements in Se leetive Circuits, of which the following ,isa full, clear, concise, and exact description.

This invention relates to highly selective electric circuits.

One object of the invention isto selective- 1y control the transmission of waves through a nircuit.

Another object is to provide a method and means for sharply discriminating between waves to be transmitted through a circuit and Waves to be excluded therefrom.

,A further object of the invention is to prevent the How of current of carrier or of other 2. frequencies through the output circuit of an amplifier, modulator, detector, or otherform .of'relay device, or similar apparatus.

It is old in the art to employ tuned circuits containing inductance and capacity to selectively transmit or suppress waves of certain frequencies in an electric circuit. Such tuned circuits are, in general, ego-n to the objection that they only partially xclude undesired waves, and are thus subj ct to definite limitations. For example, t 1e so-called antiresonant circuit consisting o a capacity reactance in shunt with an ind ctive reactance is, when the circuit contains appreciable resistance, only partially effective in prevent-v ing the flow therethrough of/waves having the same period as the circuit.

In accordance withjtbypresent invention,

a circuit is provided which completely blocks the flow of waves of one or more given frequencies and at the same time passes waves of other frequencies with any desired relative amplitude. "It has been found that by properly proportioning the constants of a tuned circuit connected between the input and output circuits of a relay, Waves of a period equal to that of the natural period of the tuned circuit may be completely or partially excluded from the output circuit of the relay. The invention is specifically applied to a thermionic relay wherein the space current between the anode and cathode 1s controlled "matic diagram showin by a grid connected to the input circuit. An equation, based upon the constants of the thermi nic tube and the connected circuits, is employed to determine the values of the constants.of the tuned circuit to be connected between the input and output circuits. By connecting several impedances, or a network, between the input and output circuits of a relay," waves of a plurality .of frequencies may be selectively suppressed or controlled.

Features of the invention, believed to be novel, are .pointed 1 but in the appended claims. The follQwing-ide'scription taken in connection with, the, "ompanying drawing specifies further objects and details of the invention.

Referring to the'drawing, Fig. 1 is a schea relay circuit arran ed in accordance wlth this invention;

Fig. 2 is a circuit diagram showing the invention as applied to a signaling sys m;

Fig. 3 is a diagram showing the relation of currents in portions of the circuit, of Fig. 2;

i Fig. 4. is a circuit diagram showing the invention as applied to a carrier wave modu lating system .in which a component of some given frequency, such as the unmodulated carrier frequency, may be eliminated from theoutput circuit;

Fig. 5' is a circuit diagram showing a method of connecting a network or a plurality of tune'cl im-pedances between the input and output circuits of a relay to limit the flow of waves of a plurality of'frequ'e'ncies;

Fig. 6 is a diagram showing variations of output current with frequency in a circuit such as that of Fig. 5. 5'

Fig. 7 is a diagram of ag'modification of the modulator shown in Fi 4, the modulating waves being impressed between the grid and anode.

In Fig.1 the space discharge device, or relay tube 1 includes the cathode 2, the anode 3, and the control electrode or grid 4. The input circuit 5.includes the source of alternating potential e in series, between the cathode 2 and the grid 4. The outputcirthe impedance Z is connected between the innut circuit 5 and the output circuit 6.

11 an article by the inventor in the Physical Review, Lancaster, PtL, N. S. volume X111, 6, June 19, 1919, page 404, it is shown th a vacuum tube such as tube 1 when conneiiied in a. circuit such as shown in Pi 1 may he considered as a virtual source of al ternating electromotive force. However, in Fig. 1 and in the other figures of the drawing, the system may be considered to have two alternating current generators connectecl-in 'series through associated alternating current resistances. In Fig. 1, for example, alternating current generator producing electromotive force E acts through impedance Z Whereas tube 1 serving as :1 source of virtual alternating electromotive force acts through the internal alternating current resistances of tube 1, In addition, the rlectromotive force of tube 1 is 180 out of phase with the electromotive force E. It has further been shown that an alternating current of a given frequency produced. by electromotive force E may be excluded from the output circuit 6 connected between the junction points, connecting one of these alternating current generators with its associeted resistance to the other alternating current generator. By tuning impedance Z, to resonance at the frequency which it is desired to exclude and by further adjusting the resistance of impedance Z to a value having the relation to the value of the alternating current resistance of tube 1 which will be explained niore fully later, the ve riation in potential of this frequency at the junction points described may be prevented. When the resistance of impedance Z, is ad justed to the proper value and when impcch' unce Z, is tuned to the frequency to be excluded, variations in the electroinotive force E of this frequency will not produce any veriations of this frequency in the current in the circuit 6 Any reactence which may exist ,hetween the plate and grid of the tube 1 may be com pensated for in the tuning of impedance Z, so that the parallel paths comprising this reactance and the impedance Z, will. form a resonant circuit for the frequency to be excluded from the output circuit 6.

It has been found that the following, equation applies to the circuit shown in Fig. 1, Where u represents the amplifying constant of thetuhe l; I, the current flowing: in the output circuit 6 in response to the alternating potential 6; and R, the alternating current resistance between the cathode '2 and the anode 3 inthe tube 1;

essence zero reactaucc of the impedance Z,, in ac cordance with the equation:

it will be seen that the numerator of the second member of the equation '1 hecolnes zero,

or in other words the current I, in the out-- put circuit of the repeater, will be zero for the frequency at which is equal to r. If

'2' he adjusted to values other tnan in accord-- ence Wlllll equation (2) above, the magnitude of the output current of the frequency at which E, is of zero reectsnce, may be varied to any desired vulue.

A method for mathematically deriving and expressing the relation between el inents of a circuit of this type, is outlined in an article by the inventor in the Physical Review, Lancaster, Pennsylvania, ll. 9 Vol. Kill, No. 6, June, 1919, page the.

it will be seen that the circuit of E. employs relay of the type which responds to impressed Wares rurying the impedance of the tube element 1, connected be tween the terminals 2, 3 of the Work circuit In order to exclude current of a given frequency from the work circuit 6, a were component of the given frequenc is transmitted from the source 6 to the terminals 2, 3 of the work circuit, this wave coinponent being of the same frequency and amplitude as the were generated by relay action between the terminals 52, 3. lines much as the Wave transmitted from the source c is, with respect to the Work circuit 6, i180 degrees out of phase with the Wave of the same frequency generated in the relay, the two waves entirely neutralize each other with reference to the worl; circuit and are thus excluded therefrom. At frequencies other than the given frequency or frequencies to be excluded from the work circuit 6, the impedance Z, may he so great to he in effect an open circuit, so that Wnves of these frequencies are reproduced in the work circuit 6 without being neutralized by :1 wave component from the source 6.

In Fig. 2. is shown one station of a dupics, or a multiplex system. The oscillutor-modulator circuit 3, rise to modulated carrier Waves, together with un modulated carrier waves, is coupled to the input circuit of the relay tube l, the output circuit 6 of which coupled to the conductor 10. which m be connected to an an "tcnna as show or to a line wire-or other transmission path. the relay 1 is preferahly an amplifier. Between the input circuit Send the output circuit (3 is connected the grid-anode circuit containing the inipedunce 11, including the inductame 12, the resistance 13, and the capacity 14.

In order to prevent the flou through the circuit of waves of sonic given frequency,

nuance say the unmodulated carrier frequency com ponent infa wave band} derived from the oscillator-modulator circuit 9, the impedance. 11 is adjusted sharply to resonance .with

this frequency, and the resistance 13 is ad-- justed until the total eifective 'resistance of theiinpedance 11 at this frequency is equai to the quotientofthe alternating current resistance R of the tube, between the anode and cathode divided by the amplification constant 9., in accordance with the equation (2); above. I

Coupledto the conductor 10 is the input circuit of the amplifying or detecting tube 16, the output circuit 17 of which is con led to the receiving device 18. The circuit 19 connected between the input circuit 15 and the output circuit 1.7 contains the impedance network Z, for preventing the flow through the circuit 17 Y of waves Within the Wave band f, or other undesired hands. If only one frequency is ,to be suppresscd'the impedance Z may be similar to the impedance 11, and will be tuned to resonance with the wave to be suppressed, While the resistance will be adjusted in accordance with the equation (2) above. In the case where several Wavesor a wave band is to be suppressed, the impedance may take the form described later in connection with Fig. 5. a

The operation of the circuit shown in Fig. 2 is as follows: Carrier Waves modulated in accordance with signals together with uninodulated carrier Waves are impressed as a Wave band f, by the oscillatormodulator 9, upon the input circult 5 of the amplifier 1, whichamplifies the aves to be transmitted and, in cooperation with the impedance 11, suppresses any undesired wave so that only the desired wave com- ;ponents are passed on to the output circuit 6 and the antenna from which the Waves are radiated. At the same time waves of frequency 7", from a distant station are being received by the antenna conductor 10, and

I are impressed upon the input circuit 15, amplified or detected by the tube 16, and

transmitted to the receiving device 18. The impedance clement Z, cooperates with the tube 16 to exclude from the output circuit 17, (listurl'iing waves derived from the conductor 10, or any Waves impressed upon the input circuit 15 which are not desired in the output circuit 17. Other circuits vsimilar'to circuit 9, 5, '1, 8, 6 and 1!), 1G, l9. l7. 18, may be coupled. to the corn ductor 10, to provide more channels than in the d'uplcx system shown, each channel being provided with impedances between the input and'output circults of the relay device to prevent the flow of undesired Waves through the output circuits.

In 3, curve 20,21, 22, designated I,,, represents the alternating currentflowing in the antenna conductor 10 over the 9 same range of Wave frequencies impressed upon the inputcirouit 5. Curve 25, indi-/ cated as 1' represents current which would flow in the antenna conductor 10 or other resonant circuit coupled to the output 7 circuit 6, if thefiinpedance 11 were not connected betiveen the input circuit 5 and the output circuit 6. impedance 11 may be very sharply tun'dfs that high selectivity is obtained, as indicated by the steep slope of the curve 23, 21, 24 between the maximum current points 23 and 24:, and the point 21 corresponding to the frequency at which no current will flow in the antenna. The low impedance of the circuits 6 and 10 to cur-- rents having the frequencies corresponding to the point 23 and to the left thereof, and to the point 24 and to the right thereof,

sired side band frequencies or frequencies adjacent to that of the unmodulated carrier wave. The portion of curve 1,, in the neighborhood of points 23, 24 as may be seen from the drawing is of such a shape that a band of wave frequencies such as a side bendot modulated Waves may be transmitted on either side of the frequency cor: responding to the point 21 with very little or no distortion. Whereas if the transmitted energy were attenuated in accordance with the antenna impedance characteristic alone as indicated by the curve P1,, the distortion of the Wave band would be considerable. In this respect theimpedance 1]. acts as a means to compensate for unequal attenuation of Waves in some other portion ofthe system. The impedance 11, which may be of relatively-s1nall dimensions, is thus enabled to perform the same function as a more elaborate tunin means in the antenna circuit 10, and consumes a negligible quantity of energy as compared with that which would be consumed by circuit means inserted directlv in'the antenna circuit 10. Another advantage resulting from the use of the impedance ll lies in the fact that the r. 1 output circuit o, and the antenna circuit 10 are of lower impedance and resistance than would be the case it Wave suppressing moans 'ucre inserted in circuit t. or 10,

in Fig. 4, the source of modulating Waves E26. together with the source of carrier waves 27 coupled to the input circuit 28 of the modulator tube 29.Whosc output circuit 30 is connected to the input circuit 28 by i'ucaus. of the impedance Z, which is adjusted to have urxfrligiible rcactance to the frequencies to be ciiminatcd, andto have a resistance as defined by equation (2) above. The output circuit 30 is connected to impress its raria- I output circuit 36.

tions upon the input circuit 31 of the amplifier 32, whose output circuit 33 is coupled to the antenna 10. Inasmuch as waves of uninodulated carrier wave frequency are suppressed before reaching the amplifier 82, the amplifier will be loaded only by energy which is to be utilized in the antenna circuit l0.

la l ig. I) is shown the relay tube 34, the input circuit 35 of which is connected to the output circuit 36 by a network Z including a resistance 37 having in series therewith a plurality of branch impedances 38. 39. 40, ll etc, connected in parallel, each of these iinpedances comprising an inductance 42 in series with a capacity 43. The re sistance 3"? is adjusted together with the induc ances 42, and the ca acities 43, so that the reactance of any given circuit path traced between the input circuit 35 and the output. circuit 36 is negligible for the ire duencies of waves which are to be eliminated in accordance with equation (2) above.

Referring to Fig. 6. the curve 44. designated as represents the output current flowing in the circuit 36, Flu. tor dit- {erent values ct frequencies impressed upon the input circuit the points 45, 48. 4?. 48, etc... being the ,trequencv values at which no current will flow in the output circuit. 36. these treoueneies being the frequencies at which paths of zero reactance are provided hetween the input circuit 35 and the It is evident from the figure that a. pluralitv of wave hands are substantially suppressed, the width of any one band being adjusted bv varying the sharpness of tuning of the corrcsp indinu' hranel. l v tuning the circuits 38. 2f), 40, 4-1, etc, to frequencies which are closer together than that designated in Fig. 6, the etl'cct ot' the various branches may be merged so that a band of i'rcuuencics may he more sharply suppressed than where a single series resonant circuit is employed.

"in "Fig. 7 a source of modulating waves 26 is coupled to the arid-anode circuit 45) of the modulator 29. Circuit 49 includes the impedance element ll similar to that disclos d in connection with Fig; 2. anode circuit 49 between the input circuit and the output circuit tuned to resonance with waves of carrierfrequency derived from the source 27. while the resistance of said circuit may be adjusted in ac cordance with eqi'iaitign (2) above. Any type or load or receiving circuit may be associated with the output circuit 3t) as, for example. the amplifier and shown in Fig. 4t. lithe resistance of the gridnnode circuit 49 be adjusted, at carrier frequency, above, waves of carrier frequency will be eliminated from the out-put circuit 30. liy adjusting the resistance of the resistance of circuit 49 is increased above {he grid-- antenna circuits in accordance with equation (2) circuit 49 to essence values different from that expressed in equation (2), any desirable amount of unrnodulated carrier wave frequency may be transmitted or suppressed, for example, as the that defined by equation (2), the component of unmodulated carrier frequency becoin'es'apprec'iable, and increases with furtherhicreases of resistance. 4

The principle of the invention has, for the P purpose of clearness, been disclosed with particular reference to specific forms of circuits and relay or repeater devices, but the invention is not limited to any of these forms, it being understood that the term relay device as used herein covers any of the devices described in a generic sense. The appended claiiris more particularly point out the nature-of the invention which .it is desired to protect.

What is claimed is:

1. In an electric circuit, a relay; device having input and output circuits, and means connected between said circuits to substantially completely prevent the flow of waves of a given frequency through said output circuit.

2. In an electric circuit, a relay device having input and output circuits, ,and an impedance elementconnected between said circuits to substantially coinpletely'pfevent the flow, of waves of given frequency through said output circuit.

v 3. In an electric circuit, a relay device having input and output circuits, 'an impcdance element connected between said circuits to preent the flow of waves of given frequency through said output circuit, the impedance of said element at said given frequency being equal to the impedance of said repeatcrdivided by the amplification constant of said relay.

4. In an electric circuit, a relay device having, input and output circuits, and an impedance element connected between said circuits to prevent the flow of waves of given frequency through said output eircuit, the reactance of said element at said given frequency being zero.

5. In an electric circuit, a relay device having input and output circuits, an inn pedance element connected between S&1(l C1I cuits to prevent the flow of waves of given frequency through said output circuit, said impedance being, in etlfect, a pure resistance at. said given frequency.

6. In an electric circuit, a thermionic r elay having an anode. a cathode, and a grid and means connected between said ,Q'lld. and anode to substantially completely prevent 125 the flowof wave energy of a given frequency from said relay.

7. In an electric circuit, a thermionic relay having" an anode, a cathode, and a grid,. and an impedance element connected becompletely prevent the fiow of wave energy of a given frequency from'said relay.

8. In an electric circuit, a thermionic relay having-an anode, a oath do, and a grid, and an impedance element connected ,between said grid and anode to, prevent the flow of wave energy of agiven, frequency from said relay, said element having an impedance at said. given frequency which bears a predetermined ratio to-the impedance of said relay.

9. In an electric circuit, a thermionic relay having an anode, a cathode, and a grid, and an impedance elementdncluding inductance, capacity, and resistance connected between said grid and a'noddto prevent the flow of wave energy of a given frequency from said relay, said resistance being'adjusted to a value as given by the equation 10. In a relay circuit of the two which responds to impressed waves by va ing the impedance of an element connected etween the terminals ofla work circuit containing a local source of energy, the method of exeluding from said work circuit a vfirst wave of given frequency and amplitude, which comprises 'impressing'upon said terminals a second wave ofvthe same frequency, and

- amplitude as said first wave, but 180 degrees out of phase therewith.

11. In athermionic relayof the type in cluding an anode, a cathode, and a grid, the

method of reducing the effect of a g1ven frequency compo ent of E. M. F. produced between the an de and cathode, which comprises impressi g an auxiliary E. M. F. across the anode'and cathode.

12. In an electric'tircuit, a relay device having input and output circuits, and an impedance element including inductance, capacity and resistance connected between said circuits to prevent the flow of waves of a given frequency through said output circuit, said resistance being of a value as determihed by equation (2).

13. In an electric circuit, a relay device having input and output circuits, and a network, having a plurality of natural periods, connected between said circuits to prevent the flow of a plurality of waves of given frequencies through said output circuit, said network including a resistance the value of which is determined by equation i4. In a modulating system, a thermionic modulator having an anode, a cathode, and a grid, an input circuit connected to said grid and cathode, and an output circuit connected to said anode and cathode, a-

source of waves of carrier and modulating frequency in said input circuit, and means connected "between said input and output circuits to prevent the flow of unmodulated waves through said output circuit.

15, In a modulating system, a thermionic modulator having an anode, a cathode, and a grid, an input circuit connected to said grid and cathode, and an output circuit connected to said anode and cathode, a source of waves of carrier and modulating fre-- quency in said input circuit, and an impedance element connected between said input and output circuits to prevent the flow of unmodula ted Waves through said output circuit o 16. In a modulting system, a thermionic modulator having an anode, a cathode, and a grid, an input circuit connected vto said gride -and cathode, and an output circuit connected to said anode and cathode, a source of waves of carrier and modulating frequency in said input circuit, an impedance element tuned to resonance with said carrier waves to prevent the flow' of un--' modulated wavesthrough'said output circuit.

17. modulator having an anode, a cathode, and agrid, an input circuit connected to said grid and cathode, and an' output circuit connectedto said anode and cathode, a source ofwaves of carrier and modulating frequency in said input circuit, an impedance eleijint tuned to resonance with said carrier waves, the effective resistance of said impedance at carrier frequency being substantially equal to the resistance of said modulator between said anode and cathode divided by the amplification constant of said modulator.

18. In an electric signaling system, a common path for a plurality of signal currents, a relay coupled to said path, said relay having input and output circuits, and means connected between said input and output circuits to. selectivel pre'vent current of given .frequency, owing in said common path,- from producing current in said output circuit.

19. In an electric. signaling system, a common path for a plurality of signal currents, a relay coupled to said path, said relay having input and-output circuits, :1 tuned circuit connected between said input and output circuits in series with a resistance having a value determined by equation (2) to selectively prevent current of given frequency, flowing in said common path. from producing current in said output circuit.

20. In an electric signaling system, a common path for a plurality of signal cur-- rents, a relay coupled to said path,-said relay having input and output circuits, a tuned circuit connected between said input and output circuits to selectively prevent In a modulating system, a thermionic given frequency messes 2-1. In on electric signaling system, c common pctli .ror a plurality of signal currents, e relay coupled to said path, seicl relay hev-; Eng input output circuits, e tuned circult connected between said input and output circuits to selectively prevent current 01% given frequency, flowing in sand common path, from producing current in seicl outjout circuit, seicl tueerl circuit containing 1r cluctencc, capacity, eml resistance, the impedance of tuned circuit being equal st Siilfl. given frequency to theimceclence of seirlrelc (fielded. by the smgilificotion constent oif eifi relay.

in electric signalling system, a transmission puih carrying Waves of given frequency, e source of Waves of enotlier couplerl to said path to imtliereon of sold other frequency, ii receiving coupled to path, receiving means including a relay hevitcpot sod output circuits, emit means between input and output c'rcuits to rezluce the flow through said outout circuit of Waves of one of said given,

lireqccrlcies.

electric signaling system, 21' tceucmissiou peels carrying Waves of givcu frequency, sour-e of 'weves of another git es frequency coo led to said. pcth to 1111- press thereon or? soul other irequeuov, receiving means coupled to said path, seicl receiving means including o relay having input 21ml output ircnits encl an imclement connected between said input and output circuits to prevent the How tlirougl': said. output circuits of Waves of one 05 said frequencies,

2%. "in combination, space discharge (levies iuclusling; E3051? cathode, and control members, means for 'lu'lpressing Wave oe- L ween two of: said members, on output circult. connected between said anode and cstliocle, and rhesus sociutecl with soil levlce for causing c Jsolute suppression of said waves from oirwput circuit.

25. In comb ilieclmrge (leiec including com curl control members, means for mg a were oetween two of soul iuemliei on output circuit connects, heirs-ecu scicl anode and cathode and an impedance clementesscci etccl with said device for causing the absolute suppression of said Waves from said output circuit 26. In a modulator system, a space (lischarge device including anode, cathode and control members, means for impressing e mmluleting Wave between two of sold memhers and u carrier Wsve between two of said members, an output circuit connected between said anode and cathode, and means associated with said device to suppress any desired amount of one 01? saicl impressed Waves from said output circuit.

2?. in a, modulating system, a space di charge device includiiig an anode, e cathode, and a control member, means for impressing a carrier wave upon said device, anal meims for impressing e wave solely between acid control member ami anode to modulate ssialcarrier were.

28. In a modulating system, as space clis' charge device including an anode, e cethofle, eml e control member, an output circuit connected between saicl enolle anal cathode, means for impressing a carrier wove upon said device, and means for imoreesin :1.

having e frequency selective, characteristic,-

end means connectcd between said. input and output fillCulllS to exclude energy of prc determined frequencies from said load circuit to compensate for the distortion profiuccd by soul load circuit. v

30. In on electric circuit, a relay device having input ancl output circuits, e loarl circuit associated with said output circuit having e frequency-selective characteristic, 21ml an impedance connected between said input and output circuits to exclude energy of pro cletermine frequencies from seicl output circuit to compensate for the (listortiou pro- (lucecl by said loarlv circuit.

81. In an electric circuit, a relay device having input and output, circuits, e source 03? oscillations hc'vingo complex wave form impressed upon sold input circuit, a. load circuit sssociatal with said output circuit having e frequency scective characteristic. eml impedance connected 'lo'etween said input and output circuits to compensate for the list/ortion produced by said load circuit. saicl impeence comprising series reactive elements tuneclto one of the frequency com-- poneuts from suicl lsource, ands series rcslsrsuce substantially equal to the internal resistance of scirl'clvice divided by the am 

